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<title>Using the GNU Compiler Collection (GCC): Java Exceptions</title>

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<a name="Java-Exceptions-1"></a>
<h3 class="section">7.12 Java Exceptions</h3>

<p>The Java language uses a slightly different exception handling model
from C++.  Normally, GNU C++ automatically detects when you are
writing C++ code that uses Java exceptions, and handle them
appropriately.  However, if C++ code only needs to execute destructors
when Java exceptions are thrown through it, GCC guesses incorrectly.
Sample problematic code is:
</p>
<div class="smallexample">
<pre class="smallexample">  struct S { ~S(); };
  extern void bar();    // <span class="roman">is written in Java, and may throw exceptions</span>
  void foo()
  {
    S s;
    bar();
  }
</pre></div>

<p>The usual effect of an incorrect guess is a link failure, complaining of
a missing routine called &lsquo;<samp>__gxx_personality_v0</samp>&rsquo;.
</p>
<p>You can inform the compiler that Java exceptions are to be used in a
translation unit, irrespective of what it might think, by writing
&lsquo;<samp>#pragma&nbsp;GCC&nbsp;<span class="nolinebreak">java_exceptions</span><!-- /@w --></samp>&rsquo; at the head of the file.  This
&lsquo;<samp>#pragma</samp>&rsquo; must appear before any functions that throw or catch
exceptions, or run destructors when exceptions are thrown through them.
</p>
<p>You cannot mix Java and C++ exceptions in the same translation unit.  It
is believed to be safe to throw a C++ exception from one file through
another file compiled for the Java exception model, or vice versa, but
there may be bugs in this area.
</p>



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